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Comment by blhack | Hacker News Reader

Why aren't we sending probes out right now? Yeah, we're not going to hear anything back for (probably) 100 years, but why not start now? If we had sent a probe out back in the 60s, this would be something that I'd see results from within my lifetime.

Of course, this is assuming that we can build fast interstellar transit systems...which is a huge if.

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Because anything we might start now would be overtaken before it is one tenth there by anything we might start five hundred years from now. And if we won't be able to start anything faster by then, there would be no technological civilization left to receive the results. So it would be pointless, space is just too big. Once we can reliably reach 1/10 c we might think about sending a probe to Alpha Centauri, although even that would have more symbolic value as a technological demonstration than scientific value. You would have to wait more than half a century for a science mission of at most a few hours, because decellerating would require so much time and fuel to make the whole mission infeasible. A mission to Gliese 581 is a distant fourth or fifth project after that, and sending a planetary probe like the one we send to mars is even more distant. (For reference, it took several years of swing by maneuvers to get a probe out of the orbital plane of the planets into an orbit that allows to examine the poles of the sun, and that takes far less energy than even reaching 1/100 c.)

It takes light 40 years to get there and back at 1,079,252,849 km/h, and the fastest spacecraft we have currently are the Helios Solar Probes at 252,792 km/h - it would take over 170,000 years before the probe returned.

Let's grant the speed of light on the return side. Say we invent a method of transmitting probe data using radio waves or something.

Getting data back via radio seems physically realistic using the gravitational lensing of EM by our sun. It would require us to put a receiving and relay station very var out beyond the planets, at least 550AU, I think. But by the time we are sending a probe several light years, then 550AU should practically be child's play.

A good paper about using such lensing: "Interstellar radio links enhanced by exploiting the Sun as a Gravitational Lens" by Claudio Maccone.

"Why aren't we sending probes out right now?"

Same reason we aren't doing a lot of other things - nobody wants to pay and sending an interstellar probe would be extremely expensive and full of engineering difficulties. It probably makes terraforming of Mars look quite feasible.

Why aren't we sending probes out right now?

Agreed. Don't send a man to do a machine's job, and this is definitely a machine's job.

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